Overclock, the main hardware is; Processor, memory and motherboard. Because these component will determine the limitation of overclock. For processor and motherboard, the limitation is the temp. High clock will increase. That will make the computer hang, or even failed to boot. But don’t worry about the temp. You can change the stock HSF the processor to other HSF which had better performance for reduce the temp.
Example :

The Air Cooling ( Schyte Infinity)

Sychte Infinity offers awesome cooling performance and is a real alternative to watercooling. In the past when I was testing at little high overclocks, The temp still keep stay in cool. For this time, Schyte infinity stil the best air cooling that I ever use.

Liquid Cooling

An uncommon practice is to submerse the computer’s components in a thermally conductive liquid. Personal computers that are cooled in this manner do not generally require any fans or pumps, and may be cooled exclusively by passive heat exchange between the computer’s parts, the cooling fluid and the ambient air. Extreme density computers such as the Cray-2 may use additional radiators in order to facilitate heat exchange.

The liquid used must have sufficiently low electrical conductivity in order for it not to interfere with the normal operation of the computer’s components. If the liquid is somewhat electrically conductive, it may be necessary to insulate certain parts of components susceptible to electromagnetic interference, such as the CPU.^[1] For these reasons, it is preferred that the liquid be dielectric.

Liquids commonly used in this manner include various liquids invented and manufactured for this purpose by 3M, such as Fluorinert. Various oils, including but not limited to cooking, motor and silicone oils have all been successfully used for cooling personal computers.

Evaporation can pose a problem, and the liquid may require either to be regularly refilled or sealed inside the computer’s enclosure. Liquid may also slowly seep into and damage components, particularly capacitors, causing a computer that initially functions to fail after hours or days immersed.